The Porsche Tire

In designing the 959, Porsche had to break new ground in many areas. In its quest for tires for their super car, Porsche asked Bridgestone in July of 1985 to design a tire that would meet the many requirements of the 959. The result was a very special edition of their high-performance RE-71 in the 235/45VR17 and 255/40VR17 sizes needed for the 959. Along the way they developed enough new technology to support 20 design patents, with patents on special rubber compounds yet to come.

One of the new design features was a different nylon cap, used to help the tire maintain the proper profile at high rpm. Unlike conventional tires, the new RE-71 uses a jointless cap for extremely high uniformity.

Over this cap Bridgestone used entirely new rubber compounds to give the 959 traction at speed while keeping down heat. A hard tire would run cool but wouldn’t handle well. A sticky tire would handle well but would self-destruct from the temperature. Misao Kawabata, Manager of Engineering for Passenger Radial Tire Development, indicated that finding these compounds was one of the major challenges in the development process.

Just to keep things interesting, Porsche had specified that the tire had to have run-flat capability. Bridgestone was able to take advantage of the built-in pneumatic sensors of the 959 and Sumitomo’s Denloc bead retention rims, but at the speeds the 959 is capable of stiffer sidewalls were also called for. The negative influence of the resulting 10 mm thick sidewalls made it necessary for Bridgestone to compensate by greatly improve other aspects of the tire, such as the shoulder profile.

The 959 is so close to a race car that one would think the tires would be close to race tires. In fact, Bridgestone has created a tire far superior to a race tire. The RE-71 will have the same speed capabilities as a F2 tire, will handle more horsepower, will take up to four times the load per tire, will last far longer, and will be suitable for use in all weather conditions.

After a year of road testing (and laboratory testing to 380 kmh) Bridgestone has certified the 17-inch RE-71 as ready. For the time being, this special RE-71 will be available only to 959 owners. The advances in tire technology, however, will most certainly spin off to other Bridgestone high performance and racing tires.